Sen. John McCain of Arizona returns to Washington, D.C., Tuesday, after being diagnosed with brain cancer last week. McCain will join his Republican colleagues as they move closer to a vote on crucial health care legislation.

“Senator McCain looks forward to returning to the United States Senate tomorrow to continue working on important legislation, including health care reform, the National Defense Authorization Act, and new sanctions on Russia, Iran and North Korea,” McCain’s office said in a statement Monday.

READ: Will McCain’s Return To Washington Help Republicans Push The Health Care Bill?

McCain’s vote is critical to Senate Majority Leader Mitch McConnell’s effort to repeal and replace, or just repeal, the Affordable Care Act, the signature law passed from the Obama administration. McConnell seeks to have a vote on a “motion to proceed,” which allows the Senate to begin discussions on a health care bill. McConnell has been secretive about what bill he would bring to the floor for discussion if a motion to proceed passes.

McConnell needs 50 votes for a motion to proceed, Vice President Mike Pence casts a tie-breaking vote. There are 52 Republicans in the Senate for McConnell to lean on, all 48 Democrats and the Independents they caucus with are opposed to the Republican plan.

Sen. Susan Collins, a Republican from Maine, has said she will not go along with the vote.

Given McCain’s diagnosis of Glioblastoma, an aggressive form of cancer, and the rush to return to the Capitol for a vote that could take health care away from millions opened up the senator for criticism on Twitter.

McCain has not yet indicated how he will vote, and calls from International Business Times to his office have not yet been returned. Many fear the Senator will toe the party line.

READ: John McCain Diagnosed With Glioblastoma, Symptoms To Know About Aggressive Brain Tumor

Over the years, President Trump has had public feuds with McCain, criticizing the former Navy pilot for being captured in the Vietnam War. On Tuesday, however, after learning he would return to Washington for a key vote, Trump praised the six-term senator.